1. Field of the Invention
The present invention relates to a method and an apparatus for the production of industrial yarns by the stretch-spinning of melt-spun polyester filaments at speeds of 3000 to 6000 m/min, stretching being carried out by means of a delivery assembly and a drawframe.
2. Prior Art Drawing Roller System
Polyester for use in the industrial sector, that is to say in an overall linear density range above 500 dtex and with a strength of at least 60 cN/tex, are produced predominantly by the stretch-spinning method which has proven highly cost-effective. Further cost savings can be achieved by increasing the productivity of the plants by raising the production speed to final speeds in the range of 6000 m/min and above. It has been shown, in addition, that filaments with new properties can also be obtained by increasing the spinning speed.
A stretch-spinning method of this type is known from U.S. Pat. No. 3,790,995. A single-stage stretch-spinning method for the production of polyester filaments is described there. This method is based on stretching between two pairs of galettes, such that, due to the absence of frictional connection between the thread and the galette surface, the stretching process on the thread commences as early as a few loopings prior to the thread leaving the delivery assembly. The stretching process is likewise terminated only a few loopings after the thread has run onto the drawing roller system. This is made possible by the roughened thread-touching surfaces of the galettes, which allows slip between the filament and the roller surface. The stretching zone is thereby effectively lengthened to a multiple of the geometrical distance between the pairs of galettes. More time is also available correspondingly for the orientation of the macromolecules forming the thread mass. A higher degree of orientation is thus achieved than when roller surfaces which are highly polished are used. Highly polished surfaces allow a maximum frictional connection between the thread and the roller surface.
Now it has been shown that, by increasing the production speed above 3000 m/min, this method no longer works optimally, since the time available for orientation is no longer sufficient. Orientation decreases in inverse proportion to the production speed. The time finally becomes so short that the high degrees of orientation necessary for use as industrial yarns can no longer be achieved. The degree of orientation is responsible for correspondingly low elongation at break and high strength of the stretched filament yarn.
The following disadvantages arise:
Lengthening the stretching time by increasing the distance between the pairs of galettes has the critical disadvantage that the overall height of the production apparatus would have to be increased to an unacceptable extent, so that the plant could no longer be operated without aids, such as lifting platforms and the like. Although the distance between the pairs of galettes can be reduced by deflecting the thread run once or more than once within the stretching zone, this nevertheless entails some serious disadvantages. Deflections within the stretching zone by means of thread guide members are undesirable and present problems. On account of the high thread pull prevailing in the stretching zone, deflecting pins and the like become very hot and lead to broken filaments even after a short operating time. Although the thread run between the pairs of galettes can be increased by means of non-driven deflecting rollers, numerous filaments breaks which make the method inefficient occur in this case. The use of deflecting rollers with a structured surface, which is known to prevent broken filaments from accumulating to form a deposit, has also not afforded any progress in this respect.